In recent years, what is called an “IP telephone” for enabling a telephone conversation through an IP network has come into wide use. A type of IP telephone that implements IP telephone functions such as call processing and audio signal processing by means of software on the PC is referred to as a softphone (see Non-patent document 1). The softphone has many advantages over an IP telephone set (hereafter referred to as a hardphone) implemented by the conventional hardware device, in terms of terminal cost, linkage with other services or functions, and the like.
Non-patent document 1: Nikkei Communications, “IP telephone ONLINE”, searched through Internet on May 16, 2005, “http://itpro.nikkeibp.co.jp/free/NCC/denwa/20050211/39/”.